Systems for delivering heated air include filtration equipment for removing particles from the air. The systems typically include mechanical filters formed from fibrous materials. The filter material functions to block particulate matter that is in the air. Particulate matter becomes attached to the filter material which, over a period of time, progressively restricts the flow of air through the filter.
The increased restriction reduces the efficiency of the heat delivery system and the effective heating of the building. The partially clogged filter also causes increased back pressure to be applied to the blower or fan which generates the air flow in forced air systems and this back pressure increases the work that must be performed and the energy consumed by the blower or fan unit. The resulting added load increases the wear rate of the moving parts in the heating system and also results in increased operating costs. Ultimately, a heavily clogged filter can cause the system to stop operating completely, create a fire hazard or fail catastrophically “dumping” the captured particles back into the airstream and into the house. Thus, it is important that partially clogged or dirty air filters are replaced promptly.
In order to determine when an air filter needs to be changed, a person typically must gain access to the filter. The filter is then removed and visually inspected. If through the visual inspection it is determined that there is a significant build up of particulate matter on the outside surface of the air filter, it is replaced with a new filter. This procedure has many problems. This procedure requires the air filter to be periodically checked in order to determine when the filter needs to be changed. This often results in dirty filters not being changed on time because people do not remember to check. Also, the mere visual inspection of the air filter does not always result in an accurate determination if the filter should be replaced. The visual inspection of the surface of the filter is not necessarily reliable in determining the condition of the filter because visible surface contamination or the lack of visible surface contamination may not be representative of contamination plugging flow paths inside the filter material.
In light of these drawbacks, many devices have been developed to determine when an air filter is dirty and needs replacement. The devices attempt to provide an indication of the need for replacement of an air filter in a heating system.
Examples of such devices are set forth in U.S. Pat. Nos. 2,753,831 and 4,321,070 which describe a device with a tube which extends through an air filter and incorporates a whistle. In these devices, air flows continuously through a tube and as the air flow through the tube increases as a result of increasing clogging of the surrounding air filter, the whistle generates a sound when the air flow rate is of a sufficient magnitude. These devices have potential problems since contamination and clogging of the tube may occur and may have a negative effect upon the operation of the whistle. Furthermore, indication by sound is not necessarily a preferable means of alerting people; for instance, with people who have difficulty hearing.
U.S. Pat. No. 2,804,839 to Hallinan discloses a device for providing a visual and audible indication of the clogging of an air filter. The device uses a magnet for retaining a pivotable member in place that provides a visual indicator and actuates a structure capable of sounding an audible alarm.
U.S. Pat. No. 6,837,922 to Gorin discloses an air filter sensor kit that includes an air filter sensor with a portion shaped for insertion through the air filter and a portion with an indicator for indicating the condition of the air filter. The kit includes an air filter sensor member for connecting the air filter sensor to an air filter grill and for supporting the air filter sensor. The kit also includes a cutting tool for cutting a hole in an air filter grill to allow the passage of a portion of the air filter sensor member to permit a portion of the air filter sensor to be inserted through the air filter.
U.S. Pat. No. 6,535,838 to Abraham et al. discloses a furnace diagnostic system and method of communicating controls and historical, as well as real-time diagnostic, information between a residential furnace controller and a portable hand held device carried by a service technician. The system includes sensors that monitor various functions of the furnace. The system provides a method of interrogating the furnace while operating, diagnosing the real time information as well as stored historical data on the furnace operations, controlling furnace components and monitoring the resulting response in real-time, and providing knowledge based troubleshooting assistance to the service technician in an expeditious manner. One embodiment of the method provides infrared communication ports on the furnace controller and handheld device to obviate the need to make physical attachments to the furnace.
U.S. Pat. No. 5,124,957 to Owens et al. discloses a programmable timing device for use in combination with an existing thermostat housing. The apparatus implements an audible and visual display to alert an individual to a need in maintenance of an associated furnace air filter. The apparatus may be secured to a wall surface or optionally, adhesively secured to the existing thermostat housing by means of a mounting bracket. A user sets a timing event with the timing mechanism to notify when the filter needs to be replaced.
The web pages, http://www.oxyfilters.com/oxy-filtergage.html, teach an indicator gage that detects reduced air flow and provides a visual indication of the need to replace the dirty air filter that can be mounted in a location up to 10 feet from a sensing location.